I expect this topic will be slow, to say the least, but any and all inquiries regarding commercial distributed audio are welcome.
I probably won't be posting much in the way of "how to" here, as I doubt there is much interest, but it is very much part of the audio world.

Our plan was to retrofit the new JBL speakers into the existing holes. Whereas the new speakers were smaller, I thought I'd make use of the old grills as trim rings, seeing as they were already painted.

Since the original install, we were called back to add a 2nd mic input so guests can plug in an addtional wireless or wired mic, as well as a line out for media box feeds or whatever.
They also added a lavalier mic, and may soon want a 2nd wireless installed.

Did another retail install last night.
All the hardware was provided, as these clients are want to do, so we showed up with wire and tools.
When we were approached for this job, it was made clear that we would receive speakers (8), a residential type tuner/amplifier, and a speaker selector switch. We would then make 8 home runs from the individual speakers back to the selector switch, and finally tie the whole mess to the amplifier.

Fuck that.

I proposed to my employer that we bring 3 conductor wire and tie the speakers in 2 home runs of 4 speakers each in a series parallel configuration. End result is the same...amplifier sees 8 ohms...all is well in the cosmos.
This would result in less material cost, less labour cost, and the client can recoup the cost of the speaker selector.
Long story short, 5 and a half hours later we have a fully functioning flush mounted in-house music reproduction system.

This morning my employer drops by the site to ensure that all expectations have been met or exceeded:

Foreman - "Where's the speaker selector?"
Us - "We didn't need it."
Foreman - "What do you mean you didn't need it?"
Us - "We wired the speakers series/parallel."
Foreman - "Oh...but every other *name* store has a speaker selector."
Us - "Wait...I'll call Montreal and see what they have to say."

*dial dial...ring ring*

Montreal - "What do you mean you didn't need it?"
Us - "We wired the speakers so that the amplifier sees 8 ohms, without the need for a speaker selector."
Montreal - "How did you do that?"
Us - "Series/ parallel."
Montreal - "What?"
Us - "With 4 speakers per side, you can wire them so that the amplifier sees the correct load."
Montreal - "But the speaker selector is part of the package. You have to use it."

So we did. We inserted the selector between the amp and the speakers. We did not run any additional wire...just 2 pairs in, 2 pairs out. The selector does nothing except degrade the signal and add more potential for future problems.

Moral:

1) The first solution installed by some junior flunkie that actually produces sound should not become the future model for a whole chain.
2) If a method of saving money and time is demonstrated, don't fight it... Embrace it. Take it to the bank.

Series/ parallel was a concept taught in the first week of Electronics 101. Hello!...McFly!
Figure it out people. It's not rocket surgery.